Position detection system

ABSTRACT

A position detecting means comprising a sensor arrangement ( 14 ) for producing at least sensor signal in a fashion dependent on a body ( 11 ) moving past said means, the sensor signal or signals continuously changing on such movement past. The at least one sensor signal is compared with at least one reference value in a comparator arrangement ( 20 ), control means being provided for electronic setting of the sensor arrangement ( 14 ) by changing the reference value and the output signal of the comparator arrangement ( 20 ) forms the position signal (P) for detection of a relative position of the body ( 11 ) and the sensor arrangement ( 14 ). Accordingly it is possible for the arrangement ( 14 ) to be mechanically set in a relatively rough manner and fine adjustment may be performed by changing the reference value electronically.

[0001] The invention relates to a position detecting means comprising asensor arrangement for producing at least one sensor signal in a mannerdependent on a body moving past the means.

[0002] Conventional position detecting means, see for example Germanpatent publication 19,504,229 A1 and more particularly those designedfor detecting a piston in a cylinder, serve to produce a position signalat one or more given piston positions by means of which the displaymeans and/or the control routines are able to be operated and,respectively, implemented. For this purpose the piston is provided witha permanent magnet and as a sensor a magnetic field sensor, moreparticularly a hall effect sensor, is employed. On moving past thepermanent magnet a sine signal is produced in the hall effect, which ina comparator is compared with a predetermined, set reference value. Ifthis reference value is reached or, respectively, exceeded, a positionsignal is generated. The sensor arrangement is normally arranged to beslid in the longitudinal direction and may be set at any desiredpositions. Since the position signal must be detected in an extremelyaccurate manner, it is necessary to provide for complex and accurateadjustment of the sensor arrangement.

[0003] One object of the present invention is to produce an exactposition signal without complex mechanical setting operations.

[0004] This object is attained in accordance with the invention by aposition detecting means with the features of claim 1 herein.

[0005] The advantage of the position detecting means of the invention ismore particularly that the sensor arrangement only needs to beapproximately fitted adjacent to the position to be detected, whereasexact setting may be performed purely electrically by changing thereference value. This is even possible by remote control. Thisadjustment may be implemented in a simple fashion by moving the movablebody, for example a piston, into the desired position in which aposition signal is to be produced, the reference value then beingchanged until the position signal is produced.

[0006] The measures recited in the dependent claims relate toadvantageous further developments of, and improvements in, the positiondetecting means recited in claim 1.

[0007] A preferred embodiment is such that the body produces a magneticfield or possesses a magnet for producing such a magnetic field and thatthe sensor arrangement comprises at least one magnetic field sensor,more particularly in the form of a hall effect sensor. In principle theinvention is however applicable to other principles of measurement, forexample to optical, to infrared or to electromagnetic measurementmethods.

[0008] In accordance with a preferred development the sensor arrangementcomprises two sensors, of which preferably the one produces a sinesignal and the other produces a cosine signal proportional to therelative position of the body and the sensor arrangement, a signalprocessing circuit being provided for conversion of such signals into asignal substantially linearly dependent on the relative position. Such asine signal and a cosine signal may for example be produced by twomagnetic field sensors, which are arranged at an angle of 45 degrees toone another. By combination of the sine signal and the cosine signal itis possible to produce a substantially linearly rising or, respectively,decaying signal, it not being the absolute amplitude but the phaserelationship which is relevant for conversion. Accordingly there is anindependence from variations in the strength of the magnetic field owingto inaccuracy of magnetic components and lack of homogeneity of themagnet and furthermore temperature dependency of the magnet.

[0009] As magnetic field sensors two hall effect sensor bridge circuitsare suitable, which are commercially available as self-containedcomplete components.

[0010] The comparator arrangement preferably possesses a windowcomparator or schmitt-trigger. Therefore it is possible for the startand end of a signal of the position signal to be adjusted. As controlmeans for changing the reference value it is more particularly suitableto employ an electrically adjustable potentiometer or a signal storagemeans for the reference value, more particularly in the form of adigital counter or a digital memory. The same may either be arrangedadjacent to the sensor arrangement and constitute a structural unit withit or however they may be arranged separate from it in space, theadjustment of the control means and/or the setting of the referencevalue then taking place by remote control by way of an electrical line,more particularly a bus, or in some wireless manner. For the adjustmentof the control means or, respectively, for setting the reference valueit is possible to provide at least one manual operating element.

[0011] The evaluating circuit comprising at least the comparatorarrangement may constitute a component group together with the sensorarrangement or it is possible for such evaluating circuit to be separatein space and more particularly be integrated in a program controlledcontrol unit. If an analog comparator arrangement is provided, it isthen possible for the digital signal from such a program controlledcontrol unit to be converted by means of a digital/analog converter intoan analog signal.

[0012] One working example of the invention is represented in thedrawing and will be described in the following account in detail. Thesingle FIGURE of the drawing diagrammatically indicates a piston andcylinder unit with a sensor arrangement and the evaluating circuitconnected with it as a working example of the invention.

[0013] In a cylinder 10 a piston 11 having a piston rod 12 is arrangedfor longitudinal motion. In the piston 11 a permanent magnet 13 isarranged.

[0014] A diagrammatically represented sensor arrangement 14 is mountedof the wall of the cylinder 19, and in a manner, which is notillustrated, is designed to be moved longitudinally and able to be setin different positions. It is naturally possible to provide more suchsensor arrangements for detecting several piston positions. The sensorarrangement or sensor arrangements may also be integrated in thecylinder's wall.

[0015] The sensor arrangement 14 comprises two hall effect sensors 15and 16, for which commercially available hall effect sensor bridges maybe employed. The hall effect sensors 15 and 16 are so positioned, forexample by being set at a relative angle of 45 degrees to one another,that under the effect of the magnetic field of the permanent magnet 13on moving past the same they supply two output signals with a phaseshift of 90 degree phase difference between them. It is of coursepossible to utilize other magnetic field sensors such as coils or thelike, which also yield two phase shifted signals, that is to say a sineand a cosine signal given a suitable positioning.

[0016] If the piston 11 moves past the sensor arrangement 14, the halleffect sensors 15 and 16 will supply a sine and cosine signalproportional to the respective setting of the permanent magnets 13 inrelation to the sensor arrangement 14. These signals are supplied to anevaluating circuit 17 and thence by way of an input amplifier 18 to asignal processing circuit 19. Instead of or in addition to the inputamplifier 18 it is also possible to provide a signal filter.

[0017] In the signal processing circuit the two signals are convertedinto a linear output signal, more particularly by the combination of thesine signal and the cosine signal. Therefore during conversion it is notthe absolute amplitude but only the phase relationship which isrelevant. This linear output signal is supplied to a comparator 20 andwhere it is compared with a variable reference value. If the signal isthe same a position signal P is produced as the output signal.

[0018] If the comparator 20 is designed in the form of a windowcomparator or schmitt trigger, the time of switching on and the time ofswitching off can be set, an adjustable hysterisis or a variable switchon and switch off threshold being provided if desired. If needed twodifferent reference signals may be produced.

[0019] The reference signal is produced by an electrically adjustablepotentiometer 21. By way of two pusch button switches 22 and 23 thereference values can be increased or reduced in size, other manualadjustment means also naturally being possible. For the adjustment thesensor arrangement 14 is moved into the approximate position, in whichthe piston 11 or, respectively, its permanent magnet 13 is to produce aposition signal. Now by operation of the pusch button switches 22 and,respectively, 23 the reference value is increased or reduced by means ofthe potentiometer as necessary until the comparator is responds. Thereference value is thus set. If necessary a second or further referencevalues may be produced in a corresponding or similar fashion.

[0020] Instead of or in addition to the pusch button switches 22 and 23the potentiometer 21 may also be set by way of an external line 24,which is connected with a connection terminal 25 of the evaluatingcircuit 17. With the aid of such an external signal, which for exampleis produced by an external control unit, which may be a programcontrolled control unit, it is possible to adjust or set thepotentiometer 21 or, respectively, the entire position detecting meansby remote control.

[0021] Instead of an adjustable potentiometer 21 it is also possible tohave a signal memory means, as for instance a digital counter or someother digital memory. The count, which sets the reference value, mayalso be set in advance by means of the pusch button switches 22 and 23and/or by way of the line 24. This will also apply for any other digitalmemory, whose stored value may also be set by way of the line 24. In thecase of a counter or other digital memory a digital/analog converter isnaturally necessary as well to be able to supply an analog referencevalue to the comparator 20. On the other hand the comparator 20 may bedesigned in the form of a digital comparator, it then being necessaryfor a corresponding digital sensor signal to be formed in the signalprocessing circuit 19.

[0022] The evaluating circuit 17 may be contained in a compactsubassembly, together with the sensor arrangement 14, able to be mountedon the cylinder 10. On the other hand it may also be arranged in anintegral manner as an external subassembly or separately. In this casethe above mentioned subassemblies of the evaluating circuit 17 may forthe most part be effected by microprocessor functions. The change in thereference value may then be performed using conventional operatingfunctions of the computer.

[0023] In accordance with a further alternative design instead of theadjustable potentiometer 21 or a signal memory means, the referencevalue for the comparator 20 is entered directly in the evaluatingcircuit 17 by way of the line 24 using an external control means or,respectively, an external computer. In the case of the line 24 it may bea question of a bus line, any necessary bus stations then having to beprovided.

[0024] The invention is naturally not limited to piston and cylinderunits, and is in fact able to be employed in all circumstances, whereany bodies are moved past sensor arrangements. Instead of detectingpositions during linear movement, non-linear motion, as for examplecircular movement, may be detected in a corresponding manner.

[0025] In order to increase the adjustment range for the electrical or,respectively, electronic adjustment, such adjustment range may also beelectrically spread.

[0026] Instead of remote control of the electrically adjustablepotentiometer 21 or some other signal memory means or instead of settingthe reference values directly by way of the line 24 it is possible forsuch operations to take place in a wireless manner, for example by radioor infrared transmission.

[0027] In an alternative design the sensor arrangement can possessseveral identical sensors or sensor combinations arranged one after theother in the direction of motion. Such sensors then produce identicaltime varying signals as well, which are offset in time in accordancewith the local offset of the sensors. At each position there will be acertain signal combination of such sensors, all signal combinationsbeing able to be detected by the signal characteristics. If now apredetermined position is to be detected, the signals stored for thisposition will be preset for a corresponding number of comparators asreference values so that the desired position may be extremely exactlydetected and errors may be detected at once. It is naturally possiblefor dimensional inaccuracies to be preset. For the electronic setting ofposition detection suitable different combinations of the referencevalues will be employed.

1. A position detecting means comprising a sensor arrangement (14) forproducing at least sensor signal in a manner dependent on a body (11)moving past the means, the at least one sensor signal changingcontinuously on such movement past the means, a comparator arrangement(20) comparing the at least one sensor signal with at least onereference value, control means being provided for electronic adjustmentof the sensor arrangement (14) by changing the reference value and theoutput signal of the comparator arrangement (20) forming the positionsignal (P) for detection of a relative position of the body (11) and thesensor arrangement (14).
 2. The position detecting means as set forth inclaim 1, characterized in that the body (11) produces a magnetic fieldor possesses a magnet (13) for the production of such a magnetic fieldand that the sensor arrangement (14) comprises at least one magneticfield sensor (15 and 16), more especially a hall effect sensor.
 3. Theposition detecting means as set forth in claim 1 on in claim 2,characterized in that the sensor arrangement (14) comprises at least twosensors, whose signals are converted in a signal processing circuit (19)into a signal dependent in a substantially linear fashion on therelative position of the body (11) and the sensor arrangement (14). 4.The position detecting means as set forth in claim 3, characterized inthat one sensor signal is a sine signal and the other signal is a cosinesignal.
 5. The position detecting means as set forth in claim 4,characterized in that two magnetic field sensors (15 and 16) arearranged at an angle of 45 degrees in relation to one another.
 6. Theposition detecting means as set forth in claim 5, characterized in thatas magnetic field sensors two hall effect sensor bridge circuits areprovided.
 7. The position detecting means as set forth in any one of thepreceding claims, characterized in that the comparator arrangement (20)possesses at least one window comparator or schmitt trigger, the twoswitching reference value being variable.
 8. The position detectingmeans as set forth in any one of claims, characterized in that thesensor arrangement (14) possesses several identical sensors or sensorcombinations arranged one after the other in the direction of motion,whose signals are compared by means of a corresponding number ofcomponents of the comparator arrangement (20) with reference values,which correspond to the sensor signals at the relative position to bedetected.
 9. The position detecting means as set forth in any one of thepreceding claims, characterized in that the control means possess anelectrically settable potentiometer (21) or a signal memory means forthe reference value and more especially a digital counter or a digitalmemory.
 10. The position detecting means as set forth in any one of thepreceding claims, characterized in that for setting the control means atleast one manual operating element (22 and 23) is provided.
 11. Theposition detecting means as set forth in any one of the precedingclaims, characterized in that the setting of the control means and/orthe setting of the reference value is remotely controlled by way of anelectrical line (24), and more especially a bus, or in a wirelessfashion.
 12. The position detecting means as set forth in any one of thepreceding claims, characterized in that the evaluating circuit (17)having at least one comparator means (20) constitutes a subassemblytogether with the sensor arrangement (14).
 13. The position detectingmeans as set forth in any one of the claims 1 through 11, characterizedin that the evaluating circuit (17) comprising at least the comparatorcircuit (17), and/or the control means are integrated in a mannerseparated in space from the sensor arrangement (14) and moreparticularly in a programmable control unit.
 14. The position detectingmeans as set forth in any one of the preceding claims, characterized inthat the body (11) is the piston of a piston and cylinder unit and thesensor arrangement (14) is integrated on the cylinder (10), moreparticularly in a longitudinally sliding manner, or in the cylinder(10).